Cathode material, preparation method thereof and lithium ion battery

Abstract

The application relates to the technical field of lithium ion battery materials, and discloses a positive electrode material, a preparation method thereof and a lithium ion battery, wherein the positive electrode material has a multilayer structure; the first layer is composed of Ni, Co, M1 and M2, the content of Ni gradually decreases from the ball center to the ball surface; the second layer is formed by Ni, Mn and M3, the content of Ni is close to that of the first layer surface; the third layer is formed by Ni, Mn and M3, the content of Mn gradually increases from the inside to the outside along the radius direction of the ball, and the content of M3 elements in the third phase gradually increases from the inside to the outside along the radius direction of the ball; M1 is Mn and / or Al; M2 is a metal oxide and / or hydroxide with an oxidation number of <=4; and M3 is a metal oxide and / or hydroxide with an oxidation number of >4. The positive electrode material with the multilayer composite structure has high capacity, good rate performance and high stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, specifically to a cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Among commonly used cathode materials, LiNiO2 is difficult to synthesize with stoichiometric products and suffers from excessively rapid capacity decay; LiCoO2 is costly, toxic, and its high-voltage, long-cycle performance needs improvement; LiMn2O4 has low specific energy and poor cycle stability; and LiFePO4 has low energy density. None of these are suitable for high-energy-density power batteries. Therefore, in recent years, nickel-cobalt-manganese / aluminum ternary cathode materials have seen some application and development due to their relatively low cost and high energy density. While the energy density of ternary materials increases to some extent with increasing nickel content, their cycle stability, thermal stability, and safety performance decrease significantly, greatly limiting the large-scale commercial application of high-nickel ternary cathodes.

[0003] In recent years, researchers have tried various methods to obtain high-nickel ternary cathode materials that combine high capacity and high stability. Common methods include doping and coating. However, these methods have not achieved ideal improvements in the electrochemical performance and stability of the materials. In addition to the above-mentioned improvement methods, new technologies and methods for material preparation have emerged. For example, designing materials as core-shell materials can significantly improve the performance of the materials. However, due to the significant differences between the core and shell materials, deep cycling can cause the core and shell to shrink / expand to different degrees during cycling, resulting in core-shell separation and loss of material effectiveness. Designing materials as full-gradient materials, where the concentration of the core and shell materials changes continuously without a clear core-shell distinction, can effectively solve this problem. However, the preparation of full-gradient precursors is difficult, and gradient vanishing is very likely to occur during the lithium sintering stage, which can also cause the material to lose its effectiveness.

[0004] To overcome these shortcomings, it is necessary to develop a cathode material with a composite structure to solve the problems faced by existing material systems. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of existing cathode materials, such as poor cycle performance, sensitivity to air, and poor thermal stability, and to provide a cathode material, its preparation method, and a lithium-ion battery. The cathode material of this invention with a multilayer composite structure has high capacity, good rate performance, and high stability.

[0006] To achieve the above objectives, the first aspect of the present invention provides a cathode material, wherein the cathode material has a multilayer composite structure, and the cathode material is a spherical or near-spherical particle formed by sequentially coating a first layer formed by a first high-nickel phase with a nickel content gradient, a second layer formed by a second nickel-manganese phase with a constant nickel content, a third layer formed by a third nickel-manganese phase with a manganese content gradient, and a coating phase formed by a fluorinated transition metal carbide coating.

[0007] The first high-nickel phase is composed of spherical or near-spherical particles made of Ni, Co, metal M1, and metal M2; wherein, in the first layer, the Ni content decreases gradually from the center of the sphere to the surface.

[0008] The second nickel-manganese phase is formed by Ni, Mn elements and metallic element M3, and covers the surface of the first high-nickel phase; wherein, the Ni content in the second layer is close to the Ni content on the surface of the first layer;

[0009] The third nickel-manganese phase is formed by Ni, Mn elements and metallic element M3, covering the surface of the second nickel-manganese phase; wherein, in the third layer, the Mn content increases from the inside to the outside along the radial direction of the sphere, and the M3 content in the third phase increases from the inside to the outside along the radial direction of the sphere.

[0010] M1 is Mn and / or Al;

[0011] M2 is a metal oxide and / or hydroxide with an oxidation number ≤ 4;

[0012] M3 is a metal oxide and / or hydroxide with an oxidation number greater than 4.

[0013] A second aspect of the present invention provides a method for preparing the aforementioned cathode material, wherein the preparation method includes:

[0014] (1) Solution preparation: Prepare two mixed salt solutions with different proportions of Ni, Co, and M1, and denot them as solution A1 and solution A2, respectively; prepare three mixed salt solutions with different proportions of Ni and Mn, and denot them as solution B1, solution C1, and solution C2, respectively; prepare a metal M2 solution, denoted as metal solution a1; prepare two metal M3 solutions with different concentrations, denoted as metal solution b1 and metal solution c1, respectively.

[0015] (2) Synthesis of the first high-nickel phase: The first solution A2 is pumped into the first solution A1, and the solution of the first solution A1, the metal solution a1 and the precipitant is pumped into a reactor containing a complexing agent as the bottom liquid, and the first coprecipitation reaction is carried out under a nitrogen atmosphere;

[0016] (3) Synthesis of the second nickel-manganese phase and the third nickel-manganese phase: After the first coprecipitation reaction, the second solution B1 and the metal solution b1 are pumped into the reactor and the second coprecipitation reaction is carried out under a nitrogen atmosphere; then the third solution C2 is pumped into the third solution C1, and the third solution C1 and the metal solution c1 are pumped into the above-mentioned reactor to carry out the third coprecipitation reaction, to obtain a solid-liquid mixture, and then the solid-liquid mixture is dehydrated, washed and dried to obtain a composite structure precursor;

[0017] (4) Coating agent modification: The coating agent with the molecular formula N n+1 Al n C n The mixture is thoroughly mixed with fluoride salt, subjected to a first heat treatment under an argon atmosphere, and then ground and sieved to obtain the modified coating agent N. n+1 C n F x ;

[0018] (5) Cathode material synthesis: The composite structure precursor is mixed evenly with the lithium source, subjected to a second heat treatment in an oxygen atmosphere, then cooled, crushed and sieved, and then mixed with the modified coating agent and subjected to a third heat treatment to prepare the cathode material.

[0019] A third aspect of the present invention provides a lithium-ion battery, wherein the positive electrode active material of the lithium-ion battery is the aforementioned positive electrode material.

[0020] Compared with the prior art, the present invention has the following superior effects through the above technical solution:

[0021] (1) The present invention uses a co-precipitation process that alternates between gradient feeding and constant concentration feeding to stably combine a first high-nickel phase with a nickel content that decreases from the inside to the outside, a second nickel-manganese phase with a nickel content close to that on the surface of the first high-nickel phase, and a third nickel-manganese phase with a manganese content that increases from the inside to the outside. This fully utilizes the high capacity characteristics of the "gradient high-nickel" phase and the high safety and high stability characteristics of the "gradient high-manganese" phase, ensuring the high capacity of the cathode material while improving the safety performance of the material.

[0022] (2) In the process of synthesizing the precursor by co-precipitation reaction, metal elements that enhance the grain growth energy barrier are introduced into the high nickel phase and metal elements that reduce the grain growth energy barrier are introduced into the nickel-manganese phase. This ensures the uniform growth of primary particles of each phase during the lithium sintering process of the precursor, strengthens the effective combination between the layered phases of different components, reduces the volume expansion and contraction differences and intergranular gaps between phases during the charging and discharging process, and effectively improves the cycle performance and thermal stability of the material.

[0023] (3) A high-conductivity and high-hydrophobic conductive protective coating is formed on the surface of the cathode material through a simple fluorinated transition metal carbide coating process, which improves the electronic conductivity of the material and enhances its air stability. Attached Figure Description

[0024] Figure 1 Here are SEM images of the composite precursor prepared in Example 1;

[0025] Figure 2 These are SEM images of the cathode material prepared in Example 1;

[0026] Figure 3 Here are SEM images of the composite precursor prepared in Example 2;

[0027] Figure 4 These are SEM images of the cathode material prepared in Example 2;

[0028] Figure 5 Here is a SEM image of the composite precursor prepared in Example 3;

[0029] Figure 6 These are SEM images of the cathode material prepared in Example 3;

[0030] Figure 7 Here is a SEM image of the composite precursor prepared in Example 4;

[0031] Figure 8 These are SEM images of the cathode material prepared in Example 4;

[0032] Figure 9 Here is a SEM image of the composite precursor prepared in Example 5;

[0033] Figure 10 These are SEM images of the cathode material prepared in Example 5;

[0034] Figure 11 The image shows a SEM image of the composite precursor prepared in Comparative Example 1.

[0035] Figure 12 This is a SEM image of the cathode material prepared in Comparative Example 1. Detailed Implementation

[0036] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0037] As mentioned above, the first aspect of the present invention provides a cathode material, wherein the cathode material has a multilayer composite structure, and the cathode material is a spherical or near-spherical particle formed by sequentially coating a first layer formed by a first high-nickel phase with a nickel content gradient, a second layer formed by a second nickel-manganese phase with a constant nickel content, a third layer formed by a third nickel-manganese phase with a manganese content gradient, and a coating phase formed by a fluorinated transition metal carbide coating.

[0038] The first high-nickel phase is composed of spherical or near-spherical particles made of Ni, Co, metal M1, and metal M2; wherein, in the first layer, the Ni content decreases gradually from the center of the sphere to the surface.

[0039] The second nickel-manganese phase is formed by Ni, Mn elements and metallic element M3, and covers the surface of the first high-nickel phase; wherein, the Ni content in the second layer is close to the Ni content on the surface of the first layer;

[0040] The third nickel-manganese phase is formed by Ni, Mn elements and metallic element M3, covering the surface of the second nickel-manganese phase; wherein, in the third layer, the Mn content increases from the inside to the outside along the radial direction of the sphere, and the M3 content in the third phase increases from the inside to the outside along the radial direction of the sphere.

[0041] M1 is Mn and / or Al;

[0042] M2 is a metal oxide and / or hydroxide with an oxidation number ≤ 4;

[0043] M3 is a metal oxide and / or hydroxide with an oxidation number greater than 4.

[0044] In this invention, it should be noted that: the first high-nickel phase can be simply referred to as the first phase; the second nickel-manganese phase can be simply referred to as the second phase; and the third nickel-manganese phase can be simply referred to as the third phase.

[0045] According to the present invention, the first high-nickel phase is a spherical or near-spherical particle composed of Ni element, Co element, metal element M1 and metal element M2; wherein, the Co element and metal element M1 are gradient distributed in the first high-nickel phase, and the M2 element is uniformly distributed in the first high-nickel phase.

[0046] According to the present invention, the second nickel-manganese phase is formed by Ni, Mn elements and metal element M3, and covers the surface of the first high-nickel phase; wherein, the M3 element is uniformly distributed in the second nickel-manganese phase.

[0047] According to the present invention, the chemical composition of the first high-nickel phase is expressed as: LiNi a Co b M1c O2-M2; where 0.60≤a≤0.98, 0.02≤b+c≤0.40, a+b+c=1.

[0048] According to the present invention, the chemical composition of the second nickel-manganese phase is expressed as: LiNi x Mn y O2-M3; where 0.60≤x≤0.80, 0.20≤y≤0.40, x+y=1.

[0049] According to the present invention, the chemical composition of the third nickel-manganese phase is expressed as: LiNi x Mn y O2-M3; where 0.60≤x≤0.80, 0.20≤y≤0.40, x+y=1.

[0050] According to the present invention, the first high-nickel phase and the second nickel-manganese phase satisfy the following:

[0051] 0.95≤n Ni1 / n Ni2 ≤1.10;

[0052] Where, n Ni1 n represents the Ni component on the surface of the first high-nickel phase. Ni2 The Ni component is the second nickel-manganese phase.

[0053] According to the present invention, the first high-nickel phase, the second nickel-manganese phase, and the third nickel-manganese phase satisfy the following:

[0054] 1.0≤D / (d1+d2)≤10.0, 6μm≤D≤16μm, 1.0μm≤d1≤3.0μm, d1<d2;

[0055] Wherein, D is the diameter of the first high-nickel phase, and d1 and d2 are the thicknesses of the second nickel-manganese phase and the third nickel-manganese phase, respectively.

[0056] According to the present invention, the chemical composition of the coated phase is expressed as N n+1 C n F x ;

[0057] The element N is selected from one of Ni, Co, Mn, Zr, Ti, Y, Nb, and Mo.

[0058] Where 1≤n≤4;

[0059] Among them, F x This indicates that all surface groups of the fluorinated transition metal carbide are replaced by -F groups with hydrophobic properties; in this invention, it should be noted that "x" represents a name, and X does not represent a specific number.

[0060] A second aspect of the present invention provides a method for preparing the aforementioned cathode material, wherein the preparation method includes:

[0061] (1) Solution preparation: Prepare two mixed salt solutions with different proportions of Ni, Co, and M1, and denot them as solution A1 and solution A2, respectively; prepare three mixed salt solutions with different proportions of Ni and Mn, and denot them as solution B1, solution C1, and solution C2, respectively; prepare a metal M2 solution, denoted as metal solution a1; prepare two metal M3 solutions with different concentrations, denoted as metal solution b1 and metal solution c1, respectively.

[0062] (2) Synthesis of the first high-nickel phase: The first solution A2 is pumped into the first solution A1, and the solution of the first solution A1, the metal solution a1 and the precipitant is pumped into a reactor containing a complexing agent as the bottom liquid, and the first coprecipitation reaction is carried out under a nitrogen atmosphere;

[0063] (3) Synthesis of the second nickel-manganese phase and the third nickel-manganese phase: After the first coprecipitation reaction, the second solution B1 and the metal solution b1 are pumped into the reactor and the second coprecipitation reaction is carried out under a nitrogen atmosphere; then the third solution C2 is pumped into the third solution C1, and the third solution C1 and the metal solution c1 are pumped into the above-mentioned reactor to carry out the third coprecipitation reaction, to obtain a solid-liquid mixture, and then the solid-liquid mixture is dehydrated, washed and dried to obtain a composite structure precursor;

[0064] (4) Coating agent modification: The coating agent with the molecular formula N n+1 Al n C n The mixture is thoroughly mixed with fluoride salt, subjected to a first heat treatment under an argon atmosphere, and then ground and sieved to obtain the modified coating agent N. n+1 C n F x ;

[0065] (5) Cathode material synthesis: The composite structure precursor is mixed evenly with the lithium source, subjected to a second heat treatment in an oxygen atmosphere, then cooled, crushed and sieved, and then mixed with the modified coating agent and subjected to a third heat treatment to prepare the cathode material.

[0066] The inventors of this invention discovered that:

[0067] (1) The first and third phases were synthesized by a gradient feeding co-precipitation method. This involved pumping a high-nickel salt solution into the reactor while simultaneously pumping a low-nickel salt solution into the high-nickel salt solution for mixing. This ensured that both solutions were fed simultaneously, achieving a radial nickel-cobalt-manganese gradient distribution within the particles of the first high-nickel phase and the third nickel-manganese phase. By using a constant-concentration feeding co-precipitation method, a second nickel-manganese phase with a nickel content close to that on the surface of the first high-nickel phase was introduced between the first and third nickel-manganese gradient phases. This formed a second nickel-manganese phase with a nickel content similar to that of the third nickel-manganese gradient phase, stably combining two layered phases with different nickel contents and compositions.

[0068] (2) In the co-precipitation reaction process, by introducing elements that enhance the grain growth energy barrier in the first high nickel phase, the reaction energy barrier in the lithium-ion sintering process is increased. In the second nickel-manganese phase and the third nickel-manganese gradient phase, elements that promote grain growth are introduced to reduce the reaction energy barrier in the lithium-ion sintering process. In the end, the uniform growth of the primary particles in the first, second and third phases is ensured under the same sintering regime.

[0069] (3) A high-conductivity and high-hydrophobicity coating layer is introduced onto the material surface simply and efficiently through a simple coating agent fluorination treatment and solid-phase sintering coating.

[0070] According to the present invention, in order to further improve the electrical properties of the material, in step (1), the molar ratio of Ni:Co:M1 in the first solution A1 is (0.90-1.00):(0.01-0.05):(0.01-0.05).

[0071] According to the present invention, in order to further improve the electrical properties of the material, in step (1), the molar ratio of Ni:Co:M1 in the first solution A2 is (0.50-0.75):(0.10-0.40):(0.01-0.10).

[0072] According to the present invention, in order to further improve the electrical properties of the material, in step (1), the total concentration of Ni, Co and M1 in the first solutions A1 and A2 is 1-10 mol / L, and the ratio of the amount of Ni in the first solution A1 to the total amount of Ni, Co and M1 is greater than that in the first solution A2.

[0073] According to the present invention, preferably, in step (1), the molar ratio of Ni to Mn in the second solution B1 is (0.50-0.75) to (0.25-0.50), and the total concentration of Ni and Mn in the second solution B1 is 1-10 mol / L.

[0074] According to the present invention, preferably, in step (1), the molar ratio of Ni to Mn in the third solution C1 is (0.50-0.75):(0.25-0.50), and the molar ratio of Ni to Mn in C2 is (0.55-0.75):(0.25-0.45). The total concentration of Ni and Mn in the third solutions C1 and C2 is 1-10 mol / L, and the molar ratio of Ni to the total molar value of Ni and Mn in the third solution C1 is greater than that in the third solution C2.

[0075] According to the present invention, preferably, the sources of Ni, Co, and M1 in step (1) can be one or more of the corresponding elements' sulfates, nitrates, acetates, oxalates, chlorides, and their hydrates.

[0076] According to the present invention, preferably, the metals M2 and M3 in step (1) can be one or more of the corresponding elements' sulfates, carbonates, and chlorides.

[0077] According to the present invention, preferably, the concentration of M2 ions in metal solution a1 in step (1) is 0.01-5 mol / L.

[0078] According to the present invention, preferably, the concentration of M3 ions in metal solution b1 in step (1) is 0.01-5 mol / L.

[0079] According to the present invention, preferably, the concentration of M3 ions in metal solution c1 in step (1) is 0.01-5 mol / L.

[0080] According to the present invention, preferably, the concentration of the precipitant solution in step (1) is 1-10 mol / L and the concentration of ammonia water is 1-10 mol / L.

[0081] According to the present invention, preferably, in step (2), the rate at which solution A2 is pumped into solution A1 is 0.1-20 L / h, the rate at which solution A1 is pumped into the reaction vessel is 0.1-20 L / h, and the rate at which metal solution a1 is pumped into the reaction vessel is 10-1000 mL / h.

[0082] According to the present invention, preferably, the precipitant in step (2) is sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate, and the complexing agent is ammonia.

[0083] According to the present invention, preferably, in step (2), the pH is 10.5-12.5, the ammonia value of the system is controlled at 1.0-10.0 g / L, the reaction temperature is 40-70℃, the stirring speed is 200-700 r / min, the time of the first coprecipitation reaction is 5-120 h, and the aging time is 1-20 h.

[0084] According to the present invention, preferably, in step (3), the second solution B1 is pumped into the reaction vessel at a rate of 0.1-20 L / h, the metal solution b1 is pumped into the reaction vessel at a rate of 10-1000 mL / h, the second coprecipitation reaction takes 5-120 h, and the aging time is 1-20 h.

[0085] According to the present invention, preferably, in step (3), the rate at which solution C2 is pumped into solution C1 is 0.1-20 L / h, the rate at which solution C1 is pumped into the reaction vessel is 2-30 L / h, the reaction temperature is 40-70℃, the stirring speed is 300-600 r / min, the initial flow rate of metal solution C1 pumped into the reaction vessel is 1-100 mL / h, and the flow rate of metal solution C1 pumped into the reaction vessel gradually decreases.

[0086] According to the present invention, preferably, the pH in step (3) is 10.0-12.5, the ammonia value of the system is controlled at 1.0-10.0 g / L, the reaction temperature is 40-70℃, the stirring speed is 200-700 r / min, and the time of the third coprecipitation reaction is 5-120 h.

[0087] According to the present invention, preferably, the drying method in step (3) is vacuum drying and forced air drying, and the drying temperature is 80-200℃.

[0088] According to the present invention, preferably, N in step (4) n+1 C n The N in the formula is one of Ti, Zr, or Y, and the fluoride salt is one of LiF, NaF, KF, CaF2, or MgF2.

[0089] According to the present invention, preferably, the first heat treatment temperature in step (4) is 500-900℃, and the first heat treatment isothermal time is 2-20h.

[0090] According to the present invention, preferably, the lithium source in step (5) is lithium hydroxide monohydrate, and the lithium hydroxide content (mass percentage) is 53.0-58.0%.

[0091] According to the present invention, preferably, the molar ratio of the precursor to lithium hydroxide monohydrate in step (5) is 1:(1-1.20).

[0092] According to the present invention, preferably, the second heat treatment in step (5) consists of a two-stage isothermal heat treatment, wherein the temperature of the first stage heat treatment is 300-600℃ and the isothermal time is 1-8h, and the temperature of the second stage heat treatment is 600-900℃ and the isothermal time is 2-20h.

[0093] According to the present invention, preferably, the mass ratio of the modified coating agent to the sieved material in step (5) is (50-100):1.

[0094] According to the present invention, preferably, the third heat treatment temperature in step (5) is 300-700℃, and the third heat treatment isothermal time is 2-20h.

[0095] A third aspect of the present invention provides a lithium-ion battery, wherein the positive electrode active material of the lithium-ion battery is the aforementioned positive electrode material.

[0096] The present invention will be described in detail below through embodiments.

[0097] For any experimental steps or conditions not specifically specified in the following examples and comparative examples, the conventional experimental procedures or conditions described in the literature in this field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available academic reagent products.

[0098] Example 1

[0099] This embodiment uses LiNi as the cathode material. 0.866 Co 0.038 Mn 0.096 O2@Ti2CF x The preparation method and specific steps are as follows:

[0100] (1) Solution preparation: Using deionized water as solvent, prepare a first solution A1 with a concentration of 8 mol / L using a molar ratio of nickel sulfate:cobalt sulfate:manganese sulfate = 0.98:0.01:0.01; prepare a first solution A2 with a concentration of 8 mol / L using a molar ratio of nickel sulfate:cobalt sulfate:manganese sulfate = 0.68:0.30:0.02; prepare a second solution B1 and a third solution C1 with a concentration of 8 mol / L using a molar ratio of nickel sulfate:manganese sulfate = 0.70:0.30; prepare a third solution C2 with a concentration of 8 mol / L using a molar ratio of nickel sulfate:manganese sulfate = 0.50:0.50; prepare a Zr solution using deionized water as solvent and zirconium sulfate as solute. 4+ A 0.02 mol / L metal solution a1; Nb was prepared using niobium sulfate as the solute. 5+ Prepare metal solutions b1 and c1 with a concentration of 0.02 mol / L; prepare sodium hydroxide solution with a concentration of 4 mol / L; prepare ammonia solutions with concentrations of 4 mol / L, 6 mol / L, and 8 mol / L respectively.

[0101] (2) First-phase synthesis: An 8 mol / L ammonia solution was added to the reactor as the base solution. The system temperature was maintained at 50°C under nitrogen protection, and the stirring speed was 700 r / min. The first solution A2 (50 L) was pumped into the first solution A1 (300 L) at a flow rate of 0.83 L / h, while the continuously stirred and mixed first solution A1 was pumped into the reactor at a flow rate of 5.83 L / h. The metal solution a1 (50 L) was pumped into the reactor at a flow rate of 833 mL / h. The feed rate of the sodium hydroxide precipitant was adjusted by negative feedback using a pH meter, and the pumping rate of the 8 mol / L ammonia complexing agent into the reactor was adjusted by negative feedback using the ammonia value of the system. During the reaction stage, the pH of the system was gradually decreased from 12.2 to 11.5, and the ammonia value of the reaction system was controlled at 4.5 g / L. After the first solutions A1 and A2 were fed in simultaneously, the mixture was stirred for 1 hour. The particle size (D50) was measured to be 8 μm using a Malvern 3000 particle size analyzer. After stirring was stopped and the mixture was aged for 10 hours, the first co-precipitated target slurry was obtained.

[0102] The chemical composition of the first phase is represented as: LiNi a Co b M1 c O2-M2. Where a = 0.9368, b = 0.0514, c = 0.0118, a + b + c = 1; where M1 is Mn and M2 is Zr.

[0103] (3) Second and third phase synthesis: A 2 mol / L second solution B1 (20 L) and a 0.02 mol / L metal solution b1 (5000 mL) were simultaneously pumped into the reactor at flow rates of 2 L / h and 500 mL / h, respectively, with a stirring speed of 600 r / min. The feed rate of sodium hydroxide precipitant was adjusted via pH meter negative feedback, and the pumping rate of 4 mol / L ammonia complexing agent into the reactor was adjusted via system ammonia value negative feedback. During the reaction stage, the system pH was gradually reduced from 12.0 to 11.0, and the system ammonia value was controlled at 4.5 g / L. After the second solution B1 and metal solution b1 were simultaneously fed, stirring was continued for 1 h. Stirring was stopped after the particle size (D50) was measured to be 9 μm using a Malvern 3000 particle size analyzer, and the mixture was aged for 5 h.

[0104] The third solution C2 (20L) was pumped into the third solution C1 (100L) at a flow rate of 0.5L / h. Simultaneously, the first solution C1, which was continuously stirred and mixed, was pumped into the reactor at a flow rate of 3L / h. The metal solution C1 was pumped into the reactor at an initial flow rate of 1.0mL / h, increasing by 2.47mL / h per hour until the flow rate reached 100mL / h. The feed rate of the sodium hydroxide precipitant was adjusted using a pH meter negative feedback, and the pumping rate of the 6mol / L ammonia complexing agent into the reactor was adjusted using a system ammonia value negative feedback. During the reaction, the pH setting of the system was gradually decreased from 11.8 to 11.0, and the ammonia value of the reaction system was controlled at 4.5g / L. After the third solutions C1, C2, and metal solution C1 were fed simultaneously, the mixture was stirred continuously for 1h. The particle size (D50) measured by a Malvern 3000 particle size analyzer was 14μm. After stirring was stopped, the third coprecipitated slurry was aged for 6 hours. It was then transferred to a centrifuge to achieve solid-liquid separation, washed with deionized water for 1 hour, dehydrated, and dried in a 120°C forced-air oven for 20 hours to obtain the composite structure precursor corresponding to the target cathode material.

[0105] The chemical composition of the second phase is represented as: LiNi x Mn y O2-M3. Where x = 0.70, y = 0.30, x + y = 1; M3 is Nb.

[0106] The chemical composition of the third phase is represented as: LiNi x Mn y O2-M3. Where x = 0.6667, y = 0.3333, x + y = 1; M3 is Nb.

[0107] Wherein, the first phase and the second phase satisfy n Ni1 / n Ni2 =0.97, where n Ni1 n is the Ni component at the surface of the first phase. Ni2 This represents the Ni component of the second phase.

[0108] The first, second, and third phases satisfy D / (d1+d2)=1.33, D=8μm, d1=1μm, d2=5μm, and d1<d2. Here, D is the diameter of the first phase, and d1 and d2 are the thicknesses of the second and third phases, respectively. The difference in thickness d1 of the second phase and d2 of the third phase leads to the final synthesized cathode material with a specific molecular formula.

[0109] (4) Coating agent modification: Ti2AlC and LiF were mixed evenly in a mixer at a mass ratio of 1:1, and then kept at 500℃ for 10h in a box furnace under an argon atmosphere. After the first heat treatment, the mixture was naturally cooled, ground, and sieved to obtain the modified coating agent Ti2CF. xF x This indicates that all surface groups of this transition metal carbide are replaced by -F groups, which have hydrophobic properties.

[0110] The chemical composition of the coated phase is represented by N. n+1 C n F x N is an element Ti. Where n = 1, F x This indicates that all surface groups of this fluorinated transition metal carbide are replaced by -F groups, which have hydrophobic properties.

[0111] (5) Synthesis of target cathode material: The precursor obtained in step (3) and lithium hydroxide monohydrate are mixed evenly in a mixer at a molar ratio of 1:1.08, and then heated in a roller kiln at 500℃ for 8 hours under an atmosphere with an oxygen concentration of ≥95%, followed by heating at 800℃ for 12 hours. After the second heat treatment, the mixture is naturally cooled, pulverized in a pulverizer, and ultrasonically sieved to obtain sieved LiNi material. 0.866 Co 0.038 Mn 0.096 O2. The sieved material is mixed with the modified coating agent Ti2CF obtained in step (4). x The materials were mixed evenly in a mixer at a mass ratio of 100:1, and then heated at 700℃ for 12 hours in a box furnace under an atmosphere with an oxygen concentration of ≥95%. After the third heat treatment, the materials were naturally cooled to obtain LiNi cathode material with a particle size of 14μm. 0.866 Co 0.038 Mn 0.096 O2@Ti2CF x Its caloric moisture content increased by 10% after 24 hours of exposure to air (RH≥50%).

[0112] in addition, Figure 1 These are SEM images of the composite precursor prepared in Example 1. Figure 1 It can be seen that the morphology of the composite structure precursor is spherical, with uniform whisker thickness, uniformly distributed gaps between whiskers, good sphericity, and smooth spherical surface.

[0113] Figure 2 These are SEM images of the cathode material prepared in Example 1. Figure 2 It can be seen that the cathode material inherits the spherical morphology of the composite structure precursor and has good primary particle uniformity.

[0114] Example 2:

[0115] This embodiment uses LiNi as the cathode material. 0.833 Co 0.061 Mn 0.106 O2@Ti2CF x The preparation method is as follows:

[0116] (1) Solution preparation: Prepare the first solution A1 with a concentration of 8 mol / L by mixing nickel sulfate:cobalt sulfate:manganese sulfate in a molar ratio of 0.95:0.02:0.03. The preparation of the remaining solutions is the same as in Example 1.

[0117] (2) First phase synthesis: An 8 mol / L ammonia solution was added to the reactor as the base liquid. The system temperature was maintained at 50°C under nitrogen protection, and the stirring speed was 700 r / min. The first solution A2 (80 L) was pumped into the first solution A1 (271 L) at a flow rate of 1.83 L / h, while the first solution A1, which was continuously stirred and mixed, was pumped into the reactor at a flow rate of 5.85 L / h. The remaining steps were the same as in Example 1, and the first coprecipitated target slurry was finally obtained.

[0118] The chemical composition of the first phase is represented as: LiNi a Co b M1 c O2-M2. Where a=0.8910, b=0.0819, c=0.0271, a+b+c=1; where M1 is Mn and M2 is Zr.

[0119] (3) Second and third phase synthesis: Same as in Example 1.

[0120] The chemical composition of the second phase is represented as: LiNi x Mn y O2-M3. Where x = 0.70, y = 0.30, x + y = 1; M3 is Nb.

[0121] The chemical composition of the third phase is represented as: LiNi x Mn y O2-M3. Where x = 0.6667, y = 0.3333, x + y = 1; M3 is Nb.

[0122] Wherein, the first phase and the second phase satisfy n Ni1 / n Ni2 =0.97, where n Ni1 n is the Ni component at the surface of the first phase. Ni2 This represents the Ni component of the second phase.

[0123] The first, second, and third phases satisfy D / (d1+d2)=1.33, D=8μm, d1=1μm, d2=5μm, and d1<d2. Here, D is the diameter of the first phase, and d1 and d2 are the thicknesses of the second and third phases, respectively. The difference in thickness d1 of the second phase and d2 of the third phase leads to the final synthesized cathode material with a specific molecular formula.

[0124] (4) Coating agent modification and target cathode material synthesis: Same as in Example 1, the final target cathode material LiNi with a particle size of 14 μm was obtained. 0.833 Co 0.061 Mn 0.106 O2@Ti2CF x The increase in caloric moisture content after 24 hours of exposure to air (RH ≥ 50%) was 7%.

[0125] in addition, Figure 3 These are SEM images of the composite precursor prepared in Example 2. Figure 3 It can be seen that the morphology of the composite precursor is spherical, the whiskers are slightly coarser than those in Example 1, the uniformity is basically the same as that in Example 1, and the gaps between the whiskers are evenly distributed.

[0126] Figure 4 These are SEM images of the cathode material prepared in Example 2. Figure 4 It can be seen that the cathode material inherits the spherical morphology of the composite structure precursor, and the primary particles have good uniformity. The primary particles are smaller than the primary cathode particles corresponding to Example 1.

[0127] Example 3

[0128] This embodiment uses LiNi as the cathode material. 0.836 Co 0.062 Mn 0.102 O2@Ti2CF x The preparation method is as follows:

[0129] The process parameters of this embodiment are basically the same as those of embodiment 2. The difference is that the flow rate of the second solution B1 in the second phase synthesis stage in step (3) is adjusted to 4L / h. The pH, ammonia value and stirring time of the system in the reaction stage are the same as those in embodiment 2. After the particle size (i.e. D50) is tested by Malvern 3000 particle size analyzer and found to be 10μm, stirring is stopped and the mixture is aged for 3h.

[0130] The chemical composition of the first phase is the same as that of the first phase in Example 2.

[0131] The chemical composition of the second phase is represented as: LiNi x Mn y O2-M3. Where x = 0.70, y = 0.30, x + y = 1; M3 is Nb.

[0132] The chemical composition of the third phase is represented as: LiNi x Mn y O2-M3. Where x = 0.6667, y = 0.3333, x + y = 1; M3 is Nb.

[0133] Wherein, the first phase and the second phase satisfy n Ni1 / n Ni2 =0.97, where n Ni1 n is the Ni component at the surface of the first phase. Ni2 This represents the Ni component of the second phase.

[0134] The first, second, and third phases satisfy D / (d1+d2)=1.33, D=8μm, d1=2μm, d2=4μm, and d1<d2. Here, D is the diameter of the first phase, and d1 and d2 are the thicknesses of the second and third phases, respectively. In this embodiment, only the flow rate is adjusted, thus controlling the total feed amount to achieve different final growth thicknesses, but the composition remains unchanged. The difference in the thickness of the second phase d1 and the third phase d2 leads to the final synthesized cathode material with a specific molecular formula.

[0135] Then, in step (3), the volume of the third solution C2 in the third phase synthesis stage was adjusted to 18L, the flow rate of C1 was adjusted to 0.45L / h, the volume of the third solution C1 was adjusted to 90L, and the flow rate of the reactor was adjusted to 2.70L / h. The pH, ammonia value, and stirring time of the reaction system were kept consistent with those in Example 2, thus obtaining the composite structure precursor corresponding to the target cathode material. Finally, after performing the same treatment as in steps (2) and (4) of Example 2, the target cathode material LiNi with a particle size of 14μm was obtained. 0.836 Co 0.062 Mn 0.102 O2@Ti2CF x The increase in caloric moisture content was 6% after 24 hours of exposure to air (RH≥50%).

[0136] in addition, Figure 5 These are SEM images of the composite precursor prepared in Example 3. Figure 5 It can be seen that the morphology of the composite precursor is spherical, and the size of the whiskers, the distribution and uniformity of the gaps between the whiskers are not much different from those in Example 1. This helps to ensure the uniform diffusion of lithium in the subsequent sintering process and ensures the uniform growth of the primary particles.

[0137] Figure 6 These are SEM images of the cathode material prepared in Example 3. Figure 6 It can be seen that the morphology of the cathode material corresponding to Example 3 is not much different from that of Example 1. Both effectively inherit the spherical morphology of the precursor. The primary particle size is not much different from that of Example 1. The primary particle size is uniform, which can ensure the uniform insertion and extraction of lithium ions in the cathode during the electrochemical reaction process.

[0138] Example 4

[0139] This embodiment uses LiNi as the cathode material. 0.850 Co 0.066 Mn 0.084 O2@Ti2CF x The preparation method and specific steps are as follows:

[0140] The process parameters of this embodiment are basically the same as those of embodiment 2. The difference is that the volume of the third solution C2 in the third phase synthesis stage in step (3) is adjusted to 10L, the flow rate of pumping C1 is adjusted to 0.25L / h, the volume of the third solution C1 is adjusted to 70L, the flow rate of pumping into the reactor is adjusted to 2.00L / h, and the pH, ammonia value and stirring time of the system in the reaction stage are kept the same as those in embodiment 2, so as to obtain the composite structure precursor corresponding to the target cathode material.

[0141] The chemical composition of the first phase is the same as that of the first phase in Example 2.

[0142] The chemical composition of the second phase is represented as: LiNi x Mn y O2-M3. Where x = 0.70, y = 0.30, x + y = 1; M3 is Nb.

[0143] The chemical composition of the third phase is represented as: LiNi x Mn y O2-M3. Where x = 0.6667, y = 0.3333, x + y = 1; M3 is Nb.

[0144] Wherein, the first phase and the second phase satisfy n Ni1 / n Ni2 =0.97, where n Ni1 n is the Ni component at the surface of the first phase. Ni2 This represents the Ni component of the second phase.

[0145] The first, second, and third phases satisfy D / (d1+d2)=2, D=8μm, d1=1μm, d2=3μm, and d1<d2. Here, D is the diameter of the first phase, and d1 and d2 are the thicknesses of the second and third phases, respectively. The difference in thickness d1 of the second phase and d2 of the third phase leads to the final synthesized cathode material with a specific molecular formula.

[0146] Finally, after performing the same treatment as steps (2) and (4) in Example 2, a target cathode material LiNi with a particle size of 12 μm was obtained. 0.850 Co 0.066 Mn 0.084 O2@Ti2CF xThe increase in calorie moisture content was 7% after 24 hours of exposure to air (RH≥50%).

[0147] in addition, Figure 7 These are SEM images of the composite precursor prepared in Example 4. Figure 7 It can be seen that the morphology of the composite precursor is spherical, and the size of the whiskers, the distribution and uniformity of the gaps between the whiskers are not much different from those in Example 1. This helps to ensure the uniform diffusion of lithium in the subsequent sintering process and ensures the uniform growth of the primary particles.

[0148] Figure 8 These are SEM images of the cathode material prepared in Example 4. Figure 8 It can be seen that the morphology of the cathode material corresponding to Example 4 is not much different from that of Example 1. Both effectively inherit the spherical morphology of the precursor. The primary particle size is not much different from that of Example 1. The primary particle size is uniform, which can ensure the uniform insertion and extraction of lithium ions in the cathode during the electrochemical reaction process.

[0149] Example 5

[0150] This embodiment uses LiNi as the cathode material. 0.866 Co 0.038 Mn 0.096 O2@Ti2CF x The preparation method and specific steps are as follows:

[0151] The same method as in Example 1 was followed, except that the ammonia value of the reaction system was controlled at 3.0 g / L during the synthesis of the first phase, and the first solutions A1 and A2 were fed in simultaneously and stirred continuously for 5 hours.

[0152] The chemical composition of the first phase is represented as: LiNi a Co b M1 c O2-M2. Where a = 0.9368, b = 0.0514, c = 0.0114, a + b + c = 1; where M1 is Mn and M2 is Zr.

[0153] During the synthesis of the second and third phases, the ammonia value of the reaction system was controlled at 3.0 g / L; wherein, the chemical composition of the second phase is expressed as: LiNi x Mn y O2-M3. Where x = 0.70, y = 0.30, x + y = 1; M3 is Nb.

[0154] The chemical composition of the third phase is represented as: LiNi x Mn y O2-M3. Where x = 0.6667, y = 0.3333, x + y = 1; M3 is Nb.

[0155] Wherein, the first phase and the second phase satisfy n Ni1 / n Ni2 =0.97, where n Ni1 n is the Ni component at the surface of the first phase. Ni2 This represents the Ni component of the second phase.

[0156] The first, second, and third phases satisfy D / (d1+d2)=1.33, D=8μm, d1=2μm, d2=4μm, and d1<d2. Here, D is the diameter of the first phase, and d1 and d2 are the thicknesses of the second and third phases, respectively.

[0157] The final target cathode material, LiNi, was obtained. 0.866 Co 0.038 Mn 0.096 O2@Ti2CF x The increase in calorie moisture content was 7% after 24 hours of exposure to air (RH≥50%).

[0158] in addition, Figure 9 These are SEM images of the composite precursor prepared in Example 5. Figure 9 It can be seen that the morphology of the composite structure precursor is spherical, the whiskers are significantly finer than those in Example 1, the gaps between the whiskers are significantly smaller than those in Example 1, and the distribution of the gaps between the whiskers is uneven. This will lead to the obstruction of lithium ion diffusion in some locations during the subsequent sintering process, resulting in uneven growth of the primary particles.

[0159] Figure 10 These are SEM images of the cathode material prepared in Example 5. Figure 10 It can be seen that the morphology of the cathode material corresponding to Example 5 is quite different from that of Example 1. Its primary particles have poor uniformity, with both extremely large and extremely small primary particles appearing at the same time. This will lead to different degrees of lithium ion extraction and insertion during the electrochemical reaction of the cathode material.

[0160] Example 6

[0161] This embodiment uses LiNi as the cathode material. 0.861 Co 0.037 Mn 0.102 O2@Ti2CF x The preparation method and specific steps are as follows:

[0162] The method is the same as in Example 1, except that the sieved material is mixed with the modified coating agent Ti2CF obtained in step (4). x The materials are mixed evenly in a mixer at a mass ratio of 20:1 to obtain the target cathode material LiNi. 0.861 Co 0.037 Mn 0.102O2@Ti2CF x .

[0163] Comparative Example 1

[0164] The comparative example is the cathode material LiNi. 0.866 Co 0.038 Mn 0.096 O2-1@Ti2CF x The preparation method is as follows:

[0165] (1) Solution preparation: Using deionized water as solvent, prepare a 2 mol / L solution D1 with a molar ratio of nickel sulfate:cobalt sulfate:manganese sulfate = 0.866:0.038:0.096, prepare a metal solution a1 with a Zr4+ concentration of 0.02 mol / L, prepare a sodium hydroxide solution with a concentration of 4 mol / L, and prepare ammonia solutions with concentrations of 4 mol / L, 6 mol / L, and 8 mol / L respectively.

[0166] (2) Precursor synthesis: An 8 mol / L ammonia solution was added to the reactor as the base liquid. The system temperature was maintained at 50°C under heating and nitrogen protection. The stirring speed was 700 r / min. Solution D1 was pumped into the reactor at a flow rate of 5.83 L / h. The feed rate of sodium hydroxide precipitant was adjusted by negative feedback using a pH meter, and the pump rate of 8 mol / L ammonia complexing agent into the reactor was adjusted by negative feedback using the ammonia value of the system. During the reaction, the pH of the system was gradually reduced from 12.2 to 11.5, and the ammonia value of the reaction system was controlled at 4.5 g / L. The particle size (D50) was measured to be 14 μm using a Malvern 3000 particle size analyzer. After that, the feeding and stirring were stopped, and the slurry D was obtained after aging for 3 h. It was then transferred to a centrifuge to achieve solid-liquid separation, washed with deionized water for 1 h, and then dehydrated. It was then dried in a 120°C forced-air oven for 20 h to obtain the composite structure precursor corresponding to the target cathode material.

[0167] (3) The process parameters for coating agent modification and target cathode material synthesis are the same as those in Example 1. The target cathode material is finally obtained, and its caloric moisture content increases by 13% after being exposed to air for 24 hours (RH≥50%).

[0168] in addition, Figure 11 These are SEM images of the composite precursor prepared in Comparative Example 1. Figure 11 It can be seen that the morphology of the composite structure precursor is spherical, the whiskers are much coarser than those in Example 1, and the gaps between the whiskers are very small. This will cause lithium ion diffusion to be hindered in some positions during the subsequent sintering process, making it very difficult for the primary particles to grow.

[0169] Figure 12 These are SEM images of the cathode material prepared in Comparative Example 1. Figure 12It can be seen that the primary particles of the cathode material corresponding to Comparative Example 1 are very small, and the grain boundaries between particles are not obvious. This will hinder the migration of lithium ions in the cathode material during the electrochemical reaction process, resulting in lower capacity and worse cycle performance.

[0170] Comparative Example 2

[0171] The comparative example is the cathode material LiNi. 0.866 Co 0.038 Mn 0.096 The preparation method of O2-2 is as follows:

[0172] (1) The solution preparation and gradient precursor synthesis were the same as those in Comparative Example 1.

[0173] (2) The precursor obtained in step (1) is mixed with lithium hydroxide monohydrate at a molar ratio of 1:1.08 in a mixer and then heated in a roller kiln at 500°C for 8 hours under an atmosphere of oxygen concentration ≥95%, and then at 800°C for 12 hours. After the second heat treatment, the mixture is naturally cooled, crushed in a pulverizer, and ultrasonically sieved to obtain the target cathode material. The increase in caloric moisture content of the material after 24 hours of exposure to air (RH≥50%) is 25%.

[0174] Comparative Example 3

[0175] The comparative example is the cathode material LiNi. 0.892 Co 0.064 Mn 0.044 The specific steps for preparing O2 are as follows:

[0176] (1) Solution preparation: It is basically the same as in Example 1, except that the first solution A1 with a concentration of 8 mol / L is prepared by molar ratio of nickel sulfate:cobalt sulfate:manganese sulfate = 0.95:0.02:0.03. The third solution, metal solution c1, is not required.

[0177] (2) Synthesis of the first phase: basically the same as in Example 5.

[0178] (3) Second-phase synthesis: A second solution B1 (250L) with a concentration of 2mol / L and a metal solution b1 (5000mL) with a concentration of 0.02mol / L were simultaneously pumped into the reactor at flow rates of 2L / h and 500mL / h, respectively, with a stirring speed of 600r / min. The feed rate of sodium hydroxide precipitant was adjusted by negative feedback using a pH meter, and the pump rate of 4mol / L ammonia complexing agent into the reactor was adjusted by negative feedback using the ammonia value of the system. During the reaction stage, the pH of the system was gradually reduced from 12.0 to 11.0, and the ammonia value of the reaction system was controlled at 4.5g / L. After the second solution B1 and the metal solution b1 were fed in simultaneously, stirring was continued for 1h. After the particle size (D50) was measured by a Malvern 3000 particle size analyzer and found to be 14μm, stirring was stopped, and the mixture was aged for 5h. Then, it was dehydrated and dried in a forced-air oven at 120℃ for 20h to obtain the composite structure precursor corresponding to the target cathode material. (3) The process parameters for coating agent modification and target cathode material synthesis are the same as those in Example 1. The target cathode material is finally obtained, and its caloric moisture content increases by 16% after being exposed to air for 24 hours (RH≥50%).

[0179] Test case

[0180] Using the material prepared by the above process as the positive electrode material, Carbon ECP600 as the conductive agent, PVDF as the binder, and NMP as the dispersant, the positive electrode material, conductive agent, and binder are weighed separately at a weight ratio of 96:2:2, mixed evenly, and the positive electrode slurry is prepared. The viscosity of the output material is controlled at around 4000 cps. Aluminum foil is used as the current collector for coating and rolling. The compaction density of the electrode sheet is controlled at 3.35 g / cm³. 3 Graphite was used as the negative electrode material, Carbon ECP600 as the conductive agent, SBR as the binder, and CMC as the thickener. These four components were weighed out separately in a weight ratio of 94.5:1.0:2.25:2.25, mixed thoroughly, and used to prepare the negative electrode slurry. The output viscosity was controlled at around 3000 cps. Copper foil was used as the current collector for coating and rolling, and the electrode compaction density was controlled at 1.30 g / cm³. 3 Celgardpp2075 was used as the separator, and the electrolyte was 2.0 mol / L LiPF6 (composed of EC+PC+EP+PP, with a mass ratio of 1:1:2:6). The positive and negative electrode sheets prepared by the above method were wound together with the separator, packaged, welded, baked, injected with electrolyte, and encapsulated to prepare 18650-2.5Ah cylindrical batteries. Formation and capacity testing were then performed, and the batteries were tested on a Xinwei testing cabinet for capacity (4.2-2.5V, 0.2C charge / discharge), rate performance (4.2-2.5V, 1C charge / 3C, 8C discharge), cycle performance (4.2-2.5V, 0.5C charge / 8C discharge), and overcharge performance (fully charged at 0.5C and then rested for 10 minutes; charged to 10V at 3C).

[0181] Among them, 3C capacity retention rate (%) is the percentage of the discharge specific capacity at 3C to the discharge specific capacity at 0.2C; 8C capacity retention rate (%) is the percentage of the discharge specific capacity at 8C to the discharge specific capacity at 0.2C; 300-cycle retention rate is the percentage of the battery discharge capacity to the discharge capacity of the battery in the first cycle after the same battery has undergone the above cycle performance test for 300 consecutive cycles; and overcharge peak temperature is the highest temperature of the battery when the above overcharge performance test is performed.

[0182] Table 1 shows the battery performance comparison results between Examples 1-6 and Comparative Examples 1-3.

[0183] Table 1

[0184]

[0185] As can be seen from the Carbide moisture gain data of Examples 1-6 and Comparative Examples 1-3, the positive electrode material of the present invention has a low Carbide moisture gain before and after exposure to air, and has better air stability.

[0186] As shown in Table 1, the specific capacity of Example 1 compared to Comparative Examples 1 and 2 is comparable to that of Comparative Examples 1 and 2 synthesized using conventional methods. The 3C retention rate is 4.2% and 7.2% higher than Comparative Examples 1 and 2, respectively, and the 8C retention rate is 6.2% and 10.2% higher than Comparative Examples 1 and 2, respectively, indicating better rate performance. The 300-cycle retention rate is 9.1% and 14.1% higher than Comparative Examples 1 and 2, respectively, indicating better cycle performance. The overcharge peak temperature is 11.3℃ and 15.5℃ lower than Comparative Examples 1 and 2, respectively, indicating better safety performance. As shown in the table, the specific capacity of Example 1 and Comparative Example 3 decreases and the rate performance deteriorates with increasing nickel-manganese phase thickness, but the cycle performance and safety are improved to some extent.

[0187] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A positive electrode material, characterized in that, The cathode material has a multilayer composite structure, and the cathode material is a spherical or near-spherical particle formed by sequentially coating a first layer of a first high-nickel phase with a gradient of nickel content, a second layer of a second nickel-manganese phase with a constant nickel content, a third layer of a third nickel-manganese phase with a gradient of manganese content, and a coating phase formed by a fluorinated transition metal carbide coating. The first high-nickel phase is composed of spherical or near-spherical particles made of Ni, Co, metal M1, and metal M2; wherein, in the first layer, the Ni content decreases gradually from the center of the sphere to the surface. The second nickel-manganese phase is formed by Ni, Mn elements and metallic element M3, and covers the surface of the first high-nickel phase; wherein, the Ni content in the second layer is close to the Ni content on the surface of the first layer; The third nickel-manganese phase is formed by Ni, Mn elements and metallic element M3, covering the surface of the second nickel-manganese phase; wherein, in the third layer, the Mn content increases from the inside to the outside along the radial direction of the sphere, and the M3 content in the third phase increases from the inside to the outside along the radial direction of the sphere. M1 is Mn and / or Al; M2 is a metal oxide and / or hydroxide with an oxidation number ≤ 4; M3 is a metal oxide and / or hydroxide with an oxidation number greater than 4.

2. The cathode material according to claim 1, wherein, M2 is selected from products containing Mg 2+ Zr 4+ Y 3+ B 3+ La 3+ Ce 3+ At least one of the oxides or hydroxides; M3 is selected from Nb 5+ Sb 5+ W 6+ Mo 6+ At least one of the oxides or hydroxides.

3. The cathode material according to claim 1 or 2, wherein, The chemical composition of the first high-nickel phase is represented as: LiNi a Co b M1 c O2-M2; where 0.60≤a≤0.98, 0.02≤b+c≤0.40, a+b+c=1; And / or, the chemical composition of the second nickel-manganese phase is expressed as: LiNi x Mn y O2-M3; where 0.60≤x≤0.80, 0.20≤y≤0.40, x+y=1; And / or, the chemical composition of the third nickel-manganese phase is expressed as: LiNi x Mn y O2-M3; where 0.60≤x≤0.80, 0.20≤y≤0.40, x+y=1.

4. The cathode material according to any one of claims 1-3, wherein, The first high-nickel phase and the second nickel-manganese phase satisfy the following: 0.95≤n Ni1 / n Ni2 ≤1.10; Where, n Ni1 n represents the Ni component on the surface of the first high-nickel phase. Ni2 The Ni component is the second nickel-manganese phase.

5. The cathode material according to any one of claims 1-4, wherein, The first high-nickel phase, the second nickel-manganese phase, and the third nickel-manganese phase satisfy the following: 1.0≤D / (d1+d2)≤10.0, 6μm≤D≤16μm, 1.0μm≤d1≤3.0μm, d1<d2; Wherein, D is the diameter of the first high-nickel phase, and d1 and d2 are the thicknesses of the second nickel-manganese phase and the third nickel-manganese phase, respectively.

6. The cathode material according to any one of claims 1-5, wherein, The chemical composition of the coated phase is represented as N n+1 C n F x ; The element N is selected from one of Ni, Co, Mn, Zr, Ti, Y, Nb, and Mo. Where 1≤n≤4; Among them, F x This indicates that all surface groups of the fluorinated transition metal carbide are replaced by -F groups, which have hydrophobic properties.

7. A method for preparing the cathode material according to any one of claims 1-6, characterized in that, The preparation method includes: (1) Solution preparation: Prepare two mixed salt solutions with different proportions of Ni, Co, and M1, and denot them as solution A1 and solution A2, respectively; prepare three mixed salt solutions with different proportions of Ni and Mn, and denot them as solution B1, solution C1, and solution C2, respectively; prepare a metal M2 solution, denoted as metal solution a1; prepare two metal M3 solutions with different concentrations, denoted as metal solution b1 and metal solution c1, respectively. (2) Synthesis of the first high-nickel phase: The first solution A2 is pumped into the first solution A1, and the solution of the first solution A1, the metal solution a1 and the precipitant is pumped into a reactor containing a complexing agent as the bottom liquid, and the first coprecipitation reaction is carried out under a nitrogen atmosphere; (3) Synthesis of the second nickel-manganese phase and the third nickel-manganese phase: After the first coprecipitation reaction, the second solution B1 and the metal solution b1 are pumped into the reactor and the second coprecipitation reaction is carried out under a nitrogen atmosphere; then the third solution C2 is pumped into the third solution C1, and the third solution C1 and the metal solution c1 are pumped into the above-mentioned reactor to carry out the third coprecipitation reaction, to obtain a solid-liquid mixture, and then the solid-liquid mixture is dehydrated, washed and dried to obtain a composite structure precursor; (4) Coating agent modification: The coating agent with the molecular formula N n+1 Al n C n The mixture is thoroughly mixed with fluoride salt, subjected to a first heat treatment under an argon atmosphere, and then ground and sieved to obtain the modified coating agent N. n+1 C n F x ; (5) Cathode material synthesis: The composite structure precursor is mixed evenly with the lithium source, subjected to a second heat treatment in an oxygen atmosphere, then cooled, crushed and sieved, and then mixed with the modified coating agent and subjected to a third heat treatment to prepare the cathode material.

8. The preparation method according to claim 7, wherein, In step (1), the molar ratio of Ni:Co:M1 in the first solution A1 is (0.90-1.00):(0.01-0.05):(0.01-0.05); And / or, the molar ratio of Ni:Co:M1 in the solution A2 is (0.50-0.75):(0.10-0.40):(0.01-0.10); And / or, the total concentration of Ni, Co and M1 in the first solution A1 and the first solution A2 is 1-10 mol / L, and the ratio of the amount of Ni in the first solution A1 to the total amount of Ni, Co and M1 is greater than that in the first solution A2.

9. The preparation method according to claim 7, wherein, In step (1), the molar ratio of Ni to Mn in the second solution B1 is (0.50-0.75):(0.25-0.50); And / or, the total concentration of Ni and Mn in the second solution B1 is 1-10 mol / L; And / or, the molar ratio of Ni to Mn in the third solution C1 is (0.50-0.75):(0.25-0.50); And / or, the molar ratio of Ni to Mn in the third solution C2 is (0.55-0.75):(0.25-0.45); And / or, the total concentration of Ni and Mn in the third solution C1 and the third solution C2 is 1-10 mol / L; And / or, the amount of Ni in the third solution C1 is greater than the total amount of Ni and Mn in the third solution C2.

10. The preparation method according to claim 7, wherein, In step (1), the ion concentration of M2 in the metal solution a1 is 0.01-5 mol / L; And / or, the concentration of M3 ions in the metal solution b1 is 0.01-5 mol / L; And / or, the concentration of M3 ions in the metal solution c1 is 0.01-5 mol / L.

11. The preparation method according to claim 7, wherein, In step (2), the precipitant is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate; And / or, the concentration of the precipitant solution is 1-10 mol / L; And / or, the complexing agent is ammonia, preferably, the concentration of the ammonia is 1-10 mol / L.

12. The preparation method according to claim 7, wherein, The first coprecipitation reaction takes 5-120 hours, and the aging time is 1-20 hours. And / or, the second coprecipitation reaction takes 5-120 hours, and the aging time is 1-20 hours; And / or, the time for the third coprecipitation reaction is 5-120 h; And / or, the first heat treatment temperature is 500-900℃, and the first heat treatment isothermal time is 2-20h; And / or, the second heat treatment consists of a two-stage isothermal heat treatment, wherein the first stage heat treatment temperature is 300-600℃ and the isothermal time is 1-8h, and the second stage heat treatment temperature is 600-900℃ and the isothermal time is 2-20h. And / or, the third heat treatment temperature is 300-700℃, and the third heat treatment isothermal time is 2-20h.

13. A lithium-ion battery, characterized in that, The positive electrode active material of the lithium-ion battery is the positive electrode material described in any one of claims 1-6.

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